1. Field of the Invention
This invention relates to an apparatus for continuously producing potassium sulfate. More particularly, it relates to an apparatus for continuously producing potassium sulfate and hydrogen chloride gas by reacting potassium hydrogen sulfate with potassium chloride.
2. Description of the Prior Art
An apparatus for continuously producing an alkali metal sulfate and hydrogen chloride gas by reacting an alkali metal chloride with sulfuric acid and/or an alkali metal hydrogen sulfate is disclosed in Japanese patent publication No. 2264/1960. This apparatus overcame the drawbacks of insufficient agitation and insufficient heat transfer of the Mannheim furnace of the vertical type employed heretofore for such a kind of reaction, by employing a horizontal type arcuate muffle furnace whereby the production capacity per unit wall surface of the heat transfer furnace was increased with an increase of 3 to 4 times that of the above-mentioned Mannheim furnace. However, the above-mentioned invention of Japanese patent publication No. 2264/1960 (which will be hereinafter referred to as prior invention) had the following four drawbacks:
1. Since the contents in the tubular furnace are heated from the total circumferential directions of the tubular furnace, the furnace material at the lower half part of the furnace where the molten reaction mixture is in close contact with the furnace is liable to be corroded.
2. Since the upper half part of the tubular furnace is different from the lower half part thereof in the heat conductive quantity per unit area, cracks of the furnace material are liable to form at the upper half part of the furnace.
3. Since heating is concentrated on the corresponding part to the initial reaction zone on the inlet side of the tubular furnace where raw materials are fed, the difference between the temperature of the inside of the furnace at that part and that of the outer casing of the furnace is much larger than the difference between the inner and outer temperatures of the furnace on the discharge side of product. Thus, cracks are liable to form at the middle part of the tubular furnace in the axial direction thereof.
4. Since the reaction mixture is much different in the composition between in the vicinity of the inlet where raw materials are fed and in the vicinity of the discharge part of product, if the retention time of the reaction mixture is made shorter than a certain critical time, the conversion decreases rapidly.
Thus, in the case of the tubular muffle furnace of the prior invention, cracks formed in the tubular furnace after continuous operation for one to several months, at a reaction temperature of 200.degree. to 450.degree. C., even when only a mixture of potassium hydrogen sulfate with potassium chloride was reacted together (note: no sulfuric acid is added at this step). As a result, disassemblying and repair of the whole of the tubular furnace have been required. In view of the above-mentioned drawbacks of the prior invention, the present inventors have made strenuous studies, and as a result have completed the invention of an apparatus capable of continuously producing potassium sulfate and concentrated hydrogen chloride for a long time and with a high efficiency.